1. Field of the Invention
The present invention relates to a magnetic sensor that detects a magnetic field by utilizing the magneto-resistance effect, a method of manufacturing the same, and an electronic device using the magnetic sensor, and more particularly, to a magnetic sensor that can detect two or more different magnetic fields, a method of manufacturing the same, and an electronic device such as a flip phone or folded-type cellular phone that can detect a displacement of a part of member such as a part of housing using the magnetic sensor.
2. Description of Related Art
A magnetic sensor that detects a magnetic field by employing the anisotropic magneto-resistance effect is called also an MR (Magneto-Resistance) sensor. The magnetic sensor is widely used in a rotation detection device that detects the rotation of an object, in a position detection device that detects the relative position between objects, and in an opening/closing detection device that detects the opening/closing of a member such as a housing of an electronic device such as a cellular phone or a notebook personal computer.
In many of the MR sensors, NiFe (permalloy) is used as an element material representing the anisotropic magneto-resistance effect. The NiFe represents desirable soft magnetic characteristics of anisotropic magnetic field of approximately 4 Oe (oersted), which is suitable as a material of a high sensitivity magnetic sensor.
Furthermore, there has been proposed a first suggestion that a magneto-resistance effect thin film which is made of a ternary alloy of NiFeCo is used as a material of a magnetic sensor (for example, refer to Patent Document 1: JP(B)-2545935, Claims, FIG. 2 and Patent Document 2: JP(A)-9-283735, Claims). The first suggestion aims at the high magneto-resistance effect and high sensitivity by the magneto-resistance effect thin film made of the ternary alloy. The magneto-resistance effect thin film of the Patent Document 1 includes Ni, Fe and Co as main components, and the composition ratio of Ni is 80% or more by weight as well as 83% or less by weight, while the composition ratio of Co is 6% or more by weight as well as 9% or less by weight, and the magnetic resistance change ratio (MR ratio) is 5.1% or more, and the anisotropic magnetic field is 10 Oe or less. However, so as to get the magnetic resistance change ratio, a heat treatment of 200° C. or more as well as 400° C. or less is necessary prior to the patterning process for the magneto-resistance effect thin film, which restricts processes. In the ferromagnetic film of a magnetic resistance element of the Patent Document 2, the composition ratio of Ni is 82% by weight, the composition ratio of Fe is 10% or more by weight as well as 12% or less by weight, and the composition ratio of Co is 6% or more by weight as well as 8% or less by weight. The ferromagnetic film has a large magnetic resistance change ratio at a lower magnetic field (1 to 2 mT [milli-tesla]) of 2 to 2.5 times that of NiFe, and a positive magneto-striction constant of +1.6×10−6.
On the other hand, there has been proposed a second suggestion that Ni1-x-y-zCozXxYy is used for a magnetic resistance element (for example, refer to Patent Document 3: JP(B)-2841657, Claims, Table, FIG. 3). In this suggestion, X is a transition metal element that is selected from Ti, V, Cr, Mn, Fe, Cu, Ag, Zn, Zr, Nb, Hf, Mo, Ta, and W, while Y is a semimetal element that is selected from B, C, Al, Si, Ge, Ga, In, and Sn, and x is 0.005 to 10 atomic %, y 0.005 to 6 atomic %, x+y 0.01 to 12 atomic %, and z is 10 to 70 atomic %. By employing the second suggestion, it becomes possible to get a magneto-resistance effect alloy and a magnetic sensor using the same, which are high in sensitivity, small in hysteresis, and small in resistance value as well as temperature coefficient of resistance change ratio.
These first and second suggestions aim at the high sensitivity in magnetic sensitivity characteristics.
A magnetic sensor is required to be provided with new functions by the device side that uses the magnetic sensor. One of the functions is a detection output function of detecting two or more different magnetic fields. This function will be explained hereunder by taking a flip phone as an example.
FIG. 15 shows a side view of a flip phone that is of the closed state and of the opened state forming an angle, and there are shown two cases of the opened state whose respective angles are different from each other. In the flip phone, a first housing 101 and second housing 102 are connected to each other via a hinge mechanism 104 so as to be opened and closed. A magnetic sensor 103 is arranged in the first housing 101, and a magnet 105 is arranged in the second housing 102. A state where the second housing 102 is in close contact with the first housing 101 is the closed state of the second housing 102 and accordingly the flip phone.
When the second housing 102 is closed, since the distance therefrom to the first housing 101 is shortest, the magnetic field detected by the magnetic sensor 103 is large. In case the first housing 101 is fixed at a position shown in FIG. 15, when the second housing 102 is opened in a direction of an arrow 106, the magnetic field detected by the magnetic sensor 103 is made small gradually. Conventionally, a point when the magnetic field detected by the magnetic sensor 103 is made equal to or smaller than a predetermined value is detected using the output voltage change, and a back light of a display, not shown, arranged on the second housing 102 is controlled to be turned on at a predetermined rotation angle corresponding to the predetermined value of magnetic field detection. In this case, the number of the value of the magnetic field detected by the magnetic sensor 103, i.e. the number of the predetermined value of magnetic field detection, may be one.
On the other hand, it is assumed that there is required a flip phone that displays first information on the display when the second housing 102 is opened by an angle θ1, and displays second information replacing the first information on the display when the second housing 102 is opened by another angle θ2. This requirement is fulfilled when the magnetic sensor 103 is of the two-output detection type that detects a predetermined first value of magnetic field in case the second housing 102 is opened by the angle θ1 with respect to the first housing 101, and detects a predetermined second value of magnetic field in case the second housing 102 is opened by another angle θ2 with respect to the first housing 101.
In this way, a magnetic sensor of the multiple magnetic field detection type that detects two or more different magnetic fields, is required to use a magnetic thin film having magneto-resistance effect characteristics which are different from those of a magnetic sensor of the conventional single magnetic field detection type. In case of a magnetic sensor of the single magnetic field detection type, for example, only a magnetic sensor of high magnetic field sensitivity that can detect a faint magnetic field has to be developed. On the other hand, in case of a magnetic sensor of the multiple magnetic field detection type, the predetermined plural values of magnetic field detection are distributed within a wide range. Accordingly, there is required a magneto-resistance effect thin film that has its magnetic resistance sufficiently changed in a wide range from the low magnetic field side to the high magnetic field side.
Especially, in case of realizing a magnetic sensor that can detect a high magnetic field of 2.5 mT [milli-tesla] or more in magnetic flux density, a conventional NiFe thin film that has its magnetic resistance changed in a narrow magnetic field range cannot attain the magnetic sensor even if the magnetic sensitivity thereof is high. Furthermore, in case of the above-mentioned NiFeCo ternary thin film by the first and second suggestions, the Patent Documents 1 to 3 do not suggest as to whether the NiFeCo ternary thin film has the magnetic resistance sufficiently changed in the above-mentioned wide range from the low magnetic field side to the high magnetic field side, or not.
Furthermore, in case of using a magneto-resistance effect thin film having a high magneto-striction constant for the magnetic sensor of the multiple magnetic field detection type, the magnetic characteristics are widely changed according to respective stresses raised in forming a film, working upon a photoresist, and packaging. As a result, it becomes difficult to set the magnetic characteristics in a targeted range, which undesirably lowers the yield ratio of the magnetic sensor. Accordingly, it is desirable to use a magneto-resistance effect thin film having a low magneto-striction constant for the magnetic sensor of the multiple magnetic field detection type.
Moreover, in obtaining magneto-resistance effect thin films, it is desired that restrictions on processes are small from a viewpoint of the cost reduction.